CN114888198A - Hot stamping forming process and stamping die - Google Patents

Abstract

The invention relates to a hot stamping forming process and a stamping die, wherein the hot stamping forming process comprises the following steps: cutting a plate, namely cutting an original plate to obtain a plate to be punched; preheating, namely preheating the plate to be punched; the first stamping is carried out, the preheated plate to be stamped is placed in a stamping die, and the first stamping is carried out on a first area of the plate to be stamped; and stamping for the second time, namely stamping for the second time on a second area of the plate to be stamped, wherein the first area and the second area are not overlapped. Compared with the traditional single hot stamping process, the method has the advantages that the first stamping is firstly carried out on the first area, the second stamping is carried out on the second area after the first stamping forming, so that the compressive stress on the sheet to be stamped is reasonably controlled, the tensile stress state can be realized, the wrinkling tendency is avoided, the dead-wrinkling area is eliminated, and the aim of reducing the wrinkling of the sheet is fulfilled; in addition, the multiple stamping process provides a variable path space, and stamping efficiency can be improved.

Description

Hot stamping forming process and stamping die

Technical Field

The invention relates to the technical field of hot stamping forming processing of metal plates, in particular to a hot stamping forming process and a stamping die.

Background

The weight reduction of automobiles has become one of the mainstream trends for the purposes of weight reduction, environmental protection and the like. The data show that the fuel can be saved by 3-7% when the weight of the automobile is reduced by 10%. And the use of the ultrahigh-strength steel can greatly improve the collision safety of the whole automobile while realizing the light weight of the automobile, so that the ultrahigh-strength steel gradually draws attention.

However, the ultra-high strength steel has high resistance and poor deformability at room temperature, and is very difficult to form by adopting the traditional cold stamping. Therefore, hot stamping is generally used for ultra-high strength steels. However, during the hot stamping process, various defects such as cracking, wrinkling, and springback inevitably occur, which seriously affect the molding quality of the material.

Disclosure of Invention

Therefore, it is necessary to provide a hot stamping forming process and a stamping die for solving the problem that the existing ultra-high strength steel is easy to wrinkle in the hot stamping forming process.

In a first aspect, the present application provides a hot stamping process, comprising the steps of:

cutting a plate, namely cutting an original plate to obtain a plate to be punched;

preheating, namely preheating the plate to be punched;

the first stamping is carried out, the preheated sheet material to be stamped is placed into a stamping die, pressure is applied to the stamping die, and the first stamping is carried out on a first area of the sheet material to be stamped;

and performing secondary stamping, namely continuously applying pressure to the stamping die, and performing secondary stamping on a second area of the plate to be stamped, wherein the first area and the second area are not overlapped.

In some embodiments, the sheet to be punched satisfies the formula L > 0.5R/t;

and L is the excess width of the plate material to be punched, R is the curvature radius of the plate material to be punched, and t is the thickness of the plate material to be punched.

In some embodiments, in the first stamping step, the first mold closing speed of the stamping mold is 100mm/s-200mm/s, the first mold closing time is 2s-5s, and the first pressure maintaining pressure is 100MPa-200 MPa.

In some embodiments, in the second stamping step, the second mold closing speed of the stamping mold is 100mm/s-200mm/s, the second mold closing time is 2s-5s, and the second pressure maintaining pressure is 100MPa-200 MPa.

In some embodiments, in the preheating step, the preheating temperature is 950 ℃ to 980 ℃ and the preheating time is 10min to 15 min.

In some embodiments, after the second stamping step, the method further comprises the steps of:

and cooling, keeping the pressure for 10-15 s after the stamping die is closed, and cooling the stamping die and the plate to be stamped in the stamping die.

In some embodiments, in the cooling step, a cooling medium is introduced into the first cooling channel and/or the second cooling channel of the stamping die to cool the plate to be stamped, and the flow rate of the cooling medium is 400L/min to 500L/min.

In a second aspect, the present application provides a stamping die for operating the hot stamping process as described above, the stamping die comprising:

the stamping die comprises a first die holder and a second die holder which are arranged at intervals along a first direction, wherein a stamping space for accommodating a plate to be stamped is formed between the first die holder and the second die holder;

the movable lower die is positioned in the stamping space and movably and convexly arranged on the surface of the first die holder facing the second die holder along the first direction;

the second die holder is provided with a concave part matched with the movable lower die, the movable lower die and the concave part are arranged corresponding to the first area, and other stamping areas on the first die holder and the second die holder are arranged corresponding to the second area.

In some embodiments, the stamping die comprises an elastic piece connected between the movable lower die and the first die holder.

In some embodiments, the resilient member is a nitrogen spring.

In some embodiments, the first die holder is provided with a first cooling channel, and/or the second die holder is provided with a second cooling channel;

and cooling media are introduced into the first cooling channel and the second cooling channel.

Compared with the traditional single hot stamping process, the hot stamping forming process and the stamping die firstly stamp the first area, stamp the second area after stamping the first area for the second time, thereby reasonably controlling the pressure stress on the sheet to be stamped, realizing the tensile stress state, avoiding the wrinkling tendency, eliminating the dead wrinkling area and further achieving the purpose of reducing the wrinkling of the sheet; in addition, the multiple stamping process provides a variable path space, and stamping efficiency can be improved.

Drawings

FIG. 1 is a flow chart of a hot stamping process according to an embodiment of the present application;

fig. 2 is a schematic overall structure diagram of a stamping die according to an embodiment of the present application;

in the figure: 100. a stamping die; 10. a first die holder; 20. a second die holder; 30. moving the lower die; 40. a stamping space; 50. an elastic member; 11. a first cooling channel; 21. a recess; 22. a second cooling channel; a. a first direction.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are not to be considered limiting of the invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and the like as used herein are for illustrative purposes only and do not denote a unique embodiment.

Fig. 1 shows a flow chart of a hot stamping forming process in an embodiment of the present invention, and fig. 2 shows an overall structural diagram of a stamping die in an embodiment of the present invention. For the purpose of illustration, the drawings show only the structures associated with embodiments of the invention.

Referring to fig. 1 and 2, an embodiment of the present invention provides a hot stamping forming process, including the steps of:

s10: and cutting the plate, namely cutting the original plate to obtain the plate to be punched.

S20: preheating, namely preheating the plate to be punched.

S30: and (3) first stamping, namely putting the preheated plate to be stamped into the stamping die 100, applying pressure to the stamping die 100, and carrying out first stamping on a first area of the plate to be stamped.

S40: and performing secondary stamping, namely continuously applying pressure to the stamping die 100, and performing secondary stamping on a second area of the plate to be stamped, wherein the first area and the second area are not overlapped.

It should be noted that in the step of S10 cutting the sheet material, the original sheet material may be cut according to the final shape of the part to be stamped, so that the target part can be better formed after the sheet material to be stamped after cutting is stamped.

Further, the plate to be punched after cutting needs to be preheated first, so that the plate to be punched is completely austenitized and is kept warm for a period of time, and a subsequent punching process is facilitated.

Specifically, the plate to be punched is placed in a heating device for preheating, wherein the heating device can be a heating furnace, that is, the plate to be punched after cutting is placed in the heating furnace and heated. Of course, in some other embodiments, the heating device may also adopt other heating structures besides the heating furnace, which is not described herein.

In actual use, many parts have relatively complex curved surface shapes. For parts with complex curved surfaces, the problems of wrinkling and the like are easily caused by adopting a single-time stamping forming process.

Based on this, after preheating is completed, the sheet material to be punched is placed in the punching die 100, the first part of the punching die 100 is firstly contacted with the first area of the sheet material to be punched, and under the action of applied external pressure, the first area of the sheet material to be punched is punched for the first time. After the first stamping is completed, pressure is continuously applied to the stamping die 100, and in the process, the first area of the plate to be stamped does not deform continuously under the support of the first part of the stamping die 100. And the second part of the stamping die 100 is in contact with the second area of the sheet material to be stamped under the action of pressure, and performs secondary stamping on the sheet material to be stamped. Thus, a complete target part is formed, and the whole stamping process is completed.

When the parts with complex curved surfaces are subjected to hot stamping forming through the steps, due to the fact that the parts are stamped at different positions of the plate to be stamped twice, the deformation process of the plate to be stamped is more stable, wrinkling is reduced, and stamping efficiency is improved.

In some embodiments, the sheet to be punched satisfies the formula L > 0.5R/t. Wherein, L is the excess width of the sheet material to be punched, R is the curvature radius of the sheet material to be punched, and t is the thickness of the sheet material to be punched.

Specifically, the original plate is generally large in area, and in order to manufacture various parts, the original plate needs to be cut so as to meet the shape requirements of target parts. However, since the plate to be stamped needs to be stamped to form the target part, the plate to be stamped deforms in the stamping process, so that the cutting size of the plate is not convenient to judge according to the final shape of the target part.

Based on the method, the size of the plate to be punched is calculated according to the formula L being larger than 0.5R/t, and then the original plate is cut according to the calculation result, so that the cutting size of the original plate can be more accurate, the problem that the plate is wasted or insufficient when a target part is formed by punching the cut plate to be punched is solved, materials are saved, and the punching efficiency can be improved.

In some embodiments, in the first stamping step of S30, the first clamping speed of the stamping die 100 is 100mm/S to 200mm/S, the first clamping time is 2S to 5S, and the first holding pressure is 100MPa to 200 MPa.

Specifically, in the first pressing step, the press mold 100 is subjected to first mold clamping under pressure. The first mold closing speed can be set to be 100-200 mm/s, the first mold closing time can be set to be 2-5 s, and the first pressure maintaining pressure can be set to be 100-200 MPa.

As one of preferred embodiments, the first clamping speed may be set to 100mm/s, the first clamping time may be set to 2s, and the first holding pressure may be set to 100MPa, so that the first portion of the press mold 100 is brought into contact with the sheet and pressed.

In some embodiments, in the step S40, in the second stamping step, the second mold closing speed of the stamping mold is 100mm/S-200mm/S, the second mold closing time is 2S-5S, and the second pressure maintaining pressure is 100MPa-200 MPa.

Specifically, in the second pressing step, the pressing die 100 continues to be pressed and subjected to the second mold clamping. The second mold closing speed can be set to be 100-200 mm/s, the second mold closing time can be set to be 2-5 s, and the second pressure maintaining pressure can be set to be 100-200 MPa.

As one of preferred embodiments, the second clamping speed may be set to 200mm/s, the second clamping time may be set to 5s, and the second holding pressure may be set to 200MPa, so that the second portion of the press mold 100 is brought into contact with the sheet and is pressed by the pressure.

In some embodiments, in the preheating step of S20, the preheating temperature is 950 ℃ to 980 ℃ and the preheating time is 10min to 15 min.

Specifically, in the preheating step, the plate to be punched needs to be heated until the plate to be punched is completely austenitized. Therefore, when the hot stamping treatment is performed on the plate materials to be stamped made of different materials, different preheating temperatures and preheating times are required.

As a preferred example, in the case of a 22MnB5 steel plate, the preheating temperature may be set to 950 ℃ to fully austenitize the 22MnB5 steel plate and the heat may be maintained for a period of time, and the preheating time for the heat may be set to 10min to facilitate the stamping process of the 22MnB5 steel plate.

In some embodiments, after the step of pressing for the second time at S40, the method further includes the steps of:

s50: and cooling, keeping the pressure for 10-15 s after the stamping die 100 is closed, and cooling the stamping die 100 and the plate to be stamped in the stamping die.

After the stamping is completed, the formed part needs to be quenched in the die so as to enable the structure of the formed part to be stable. Further, in the cooling step, cooling the plate to be stamped by introducing a cooling medium into the first cooling channel 11 and/or the second cooling channel 22 of the stamping die 100, wherein the flow rate of the cooling medium is 400L/min-500L/min.

Specifically, the cooling medium may be cooling water, that is, cooling water is introduced into the first cooling channel 11 and/or the second cooling channel 22 of the stamping die 100 to cool, and the flow rate of the cooling water is controlled to be 400L/min to 500L/min, so as to ensure sufficient cooling of the internal parts of the stamping die 100.

In a preferred embodiment, after the mold closing of the press mold 100, the pressure is maintained for 15s, and at the same time, cooling water is introduced into the press mold 100 to reduce the temperature, and the flow rate of the cooling water is controlled to be 500L/min, so as to open the mold and take out the workpiece.

Based on the same concept as the hot press forming process described above, the present application provides a press mold 100 for operating the hot press forming process as described above.

Referring to fig. 2 again, the stamping die 100 includes a first die holder 10, a second die holder 20, and a movable lower die 30, wherein the first die holder 10 and the second die holder 20 are disposed at an interval along a first direction a, and a stamping space 40 for accommodating a plate to be stamped is formed at an interval therebetween. The movable lower die 30 is disposed in the stamping space 40 and is movably protruded from a surface of the first die holder 10 facing the second die holder 20 along the first direction a. The second die holder 20 is provided with a recess 21 corresponding to the movable lower die 30, the movable lower die 30 and the recess 21 are provided corresponding to a first region, and the other press regions of the first die holder 10 and the second die holder 20 are provided corresponding to a second region.

Specifically, the first die holder 10 and the second die holder 20 are arranged at an interval, and a to-be-stamped sheet is placed in the stamping space 40 between the first die holder 10 and the second die holder 20, so that the to-be-stamped sheet is clamped in the stamping space 40 by the first die holder 10 and the second die holder 20 along the first direction a.

Pressure is applied to the first mold base 10 and the second mold base 20 to move the first mold base 10 and the second mold base 20 toward each other, and the mold closing process is performed. When pressure is applied for the first time, the movable lower die 30 protrudes out of the surface of the first die holder 10 facing the second die holder 20, so that the movable lower die 30 is firstly contacted with a sheet to be punched, and the sheet to be punched is subjected to first die closing molding under the support of the movable lower die 30. In the process, the movable lower die 30 is matched with the concave part 21, and the first region of the plate to be punched is punched for the first time.

After the first stamping, the first area of the plate to be stamped is formed in a stamping mode. Further, pressure continues to be applied to the first die holder 10 and the second die holder 20, causing the first die holder 10 and the second die holder 20 to continue to move toward each other. At this time, the first area of the sheet to be punched does not deform continuously under the support of the movable lower die 30, and the other positions on the first die holder 10 and the second die holder 20 are closed continuously under the action of pressure, so that the integral closing of the first die holder 10 and the second die holder 20 is realized. At this time, the sheet to be punched is integrally contacted with the first die holder 10 and the second die holder 20, and the other areas except the movable lower die 30 perform secondary punching on the second area of the sheet to be punched.

The plate to be punched is independently punched twice, and an integrated hot stamping process of parts with complex multi-curvature curved surfaces can be realized, so that the stamping efficiency is improved, the die cost can be reduced, and the cost input is reduced.

In some embodiments, the stamping die 100 includes an elastic member 50, and the elastic member 50 is connected between the movable lower die 30 and the first die holder 10. The elastic part 50 can provide buffer for the plate to be punched in the first punching and second punching processes, reduce the compressive stress on the plate to be punched in the punching process, and avoid the plate to be punched from being broken.

In some embodiments, the resilient member 50 is a nitrogen spring. Of course, in some other embodiments, the elastic element 50 may also adopt other spring structures, which are not described herein.

Furthermore, a first cooling channel 11 is formed in the first die holder 10, and/or a second cooling channel 22 is formed in the second die holder 20, and cooling media are introduced into both the first cooling channel 11 and the second cooling channel 22.

In the present embodiment, the cooling medium may be cooling water. It is understood that the cooling medium may be made of other materials besides cooling water, and the details are not described herein.

Specifically, a first cooling channel 11 is formed in the first die holder 10 in a penetrating manner in a direction perpendicular to the first direction a, cooling water is introduced into the first cooling channel 11, and the stamped sheet is cooled to facilitate die opening and part taking.

Similarly, a second cooling channel 22 is formed in the second die holder 20 in a direction intersecting the first direction a, and cooling water is introduced into the second cooling channel 22 to be matched with the first cooling channel 11 to achieve cooling, so that the cooling efficiency can be improved.

Specifically, a 22MnB5 steel sheet having a thickness of 0.5mm will be described as an example. Firstly, cutting an original plate according to the L larger than 0.5R/t to obtain a plate to be punched with a proper size. And (3) putting the plate to be punched into a heating furnace, heating to 950 ℃ to ensure that the plate is completely austenitized, and preserving heat for 10 min.

And transferring the preheated plate to be punched to a punching die 100, and applying pressure to the first die holder 10 and the second die holder 20 to carry out primary die assembly. In the process, the first mold closing speed is controlled to be 100mm/s, the first mold closing time is controlled to be 2s, and the first pressure maintaining pressure is controlled to be 100 MPa. Therefore, the first area of the plate to be punched is punched for the first time under the support of the movable lower die 30.

After the first punching, pressure is continuously applied to the first die holder 10 and the second die holder 20, and the dies are closed for the second time. At this time, the second mold clamping speed was controlled to 200mm/s, the second mold clamping time was controlled to 5s, and the second holding pressure was controlled to 200 MPa. In the second stamping process, the first area on the sheet to be stamped is not deformed continuously under the supporting action of the movable lower die 30, so that other areas except the first area on the sheet to be stamped, namely the second area, are deformed continuously under the die assembly action of the first die holder 10 and the second die holder 20, and finally the shape of the target part is formed.

And after the second punching, introducing cooling water into the first cooling channel 11 and the second cooling channel 22 for cooling so as to open the die and take out the workpiece.

In addition, the mechanical properties of the parts manufactured by the hot stamping forming process are verified and analyzed, and the parts are found to meet experimental expectations, and the tensile strength reaches more than 1300 MPa.

The hot stamping forming process and the stamping die 100 in the above embodiments have at least the following advantages:

1) the first area and the second area of the plate to be punched are punched and formed sequentially through twice punching, so that the wrinkling probability during the forming of the complex curved surface is reduced, the integrated hot punching process of the complex multi-curvature multi-curved surface is realized, the punching efficiency is improved, the die cost is reduced, and the cost investment is reduced;

2) and cutting the original plate material according to the calculation result of the formula L being more than 0.5R/t and obtaining the plate material to be punched, so that the plate material to be punched forms a target part with a proper size after being punched, the waste of the plate material is reduced, and the problem of insufficient plate material after the target part is formed is avoided.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (11)

1. A hot stamping forming process is characterized by comprising the following steps:

cutting a plate, namely cutting an original plate to obtain a plate to be punched;

preheating, namely preheating the plate to be punched;

the first stamping is carried out, the preheated sheet material to be stamped is placed into a stamping die, pressure is applied to the stamping die, and the first stamping is carried out on a first area of the sheet material to be stamped;

and performing secondary stamping, namely continuously applying pressure to the stamping die, and performing secondary stamping on a second area of the plate to be stamped, wherein the first area and the second area are not overlapped.

2. The hot stamping forming process according to claim 1, wherein the sheet to be stamped satisfies the formula L > 0.5R/t;

and L is the excess width of the plate material to be punched, R is the curvature radius of the plate material to be punched, and t is the thickness of the plate material to be punched.

3. The hot press forming process according to claim 1, wherein in the first pressing step, the first mold closing speed of the press mold is 100mm/s to 200mm/s, the first mold closing time is 2s to 5s, and the first holding pressure is 100MPa to 200 MPa.

4. The hot press forming process according to claim 1, wherein in the second pressing step, the second clamping speed of the press die is 100mm/s to 200mm/s, the second clamping time is 2s to 5s, and the second holding pressure is 100MPa to 200 MPa.

5. The hot stamping forming process according to claim 1, wherein in the preheating step, the preheating temperature is 950 ℃ to 980 ℃ and the preheating time is 10min to 15 min.

6. The hot press forming process according to claim 1, further comprising, after the second pressing step, the steps of:

and cooling, keeping the pressure for 10-15 s after the stamping die is closed, and cooling the stamping die and the plate to be stamped in the stamping die.

7. The hot stamping forming process according to claim 6, wherein in the cooling step, a cooling medium is introduced into the first cooling channel and/or the second cooling channel of the stamping die to cool the plate to be stamped, and the flow rate of the cooling medium is 400L/min-500L/min.

8. A stamping die for operating the hot stamping process according to any of claims 1 to 7, the stamping die comprising:

the stamping die comprises a first die holder and a second die holder which are arranged at intervals along a first direction, wherein a stamping space for accommodating a plate to be stamped is formed between the first die holder and the second die holder;

the movable lower die is positioned in the stamping space and movably and convexly arranged on the surface of the first die holder facing the second die holder along the first direction;

the second die holder is provided with a concave part matched with the movable lower die, the movable lower die and the concave part are arranged corresponding to the first area, and other stamping areas on the first die holder and the second die holder are arranged corresponding to the second area.

9. The stamping die of claim 8, wherein the stamping die includes a resilient member connected between the drag die and the first die shoe.

10. The stamping die of claim 9, wherein the resilient member is a nitrogen spring.

11. The stamping die of claim 8, wherein the first die holder is provided with a first cooling channel and/or the second die holder is provided with a second cooling channel;

and cooling media are introduced into the first cooling channel and the second cooling channel.

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